Method of recovering potassium sulfate and alumina from alunite.



H. F. CHAPPELL. METHOD OF RECOVERING POTASSIUM SULFATE AND ALUMINA FROM ALUNITE.

APPLICATION FILED JULY 23. 913.

Patented June 4;, 1918.

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HOWARD 1E. CPELL OF NEW YORK, N. Y., ASS IGNOR TO MINERAL PRODUCTS CORPO- TION, OF NEW YORK, N. Y., A CORPORATION OF MAINE.

METHOD OF BECOVERING- POTASSIUM SULFATE AND ALUMINA FROM ALUNITE.

Application filed July 23, 1913.

To all wkom it may concern:

7 Be it known that I, HOWARD F. GHAPPE L, a citizen of the United States, residing in the borough of Manhattan, city, county, and State of New York, have invented certain new and useful Improvements in Methods of Recovering Potassium Sulfate and Alumina from Alunite; and I do hereby declare the following to be a full, clear, andexact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

In an application for .Letters Patent of the United States, filed by me under date of May 8, 1913, Serial No. 766,269, I have described and shown certain improvements in the roasting or calcining of alunite, wherein the roasted product, hot from the heat of calcining, is discharged into a dissolver, that is to say, into a receptacle wherein the potash salts contained in the roasted alunite are brought into solution. In this roasting operation the aluminum sulfate is broken up, yielding-alumina while the potassium sulfate remains as such.

The present invention relates to the treat- I .In the preferred practice of the invention,

the roasted alunite is conducted hot from the heat of roasting or calcining into the dissolver, wherein the potash salts go into solution. From the dissolver, the potash salt solution passes through a filter, and is then cooled in a cooling tower. The cooling of the liquor lessens its capacity for maintaining the potash salt in solution, and, as a consequence thereof, a large proportion ofj the potash salt is deposited out of the solution.

The mother liquor, that is to say, the liquor from which the potash salts have been deposited and which still contains in solution a minor proportion. thereof is then freed from the deposited salts in any suitable way,

.as, for instance,by filtering or centrifugalizing, and is then" ready to be returned to the dlssolver.

In order to bring up to the desired maxi- Speciflcation of Letters Patent.

Patented June 41, 1918.

Serial No. 780,665.

mum the dissolving power of this mother liquor, its temperature is raised, and, as hereinbefore indicated, this is conveniently and economically efi'ected' by the heat .of the roasted alunite. Thus, the mother liquor on its return to the dissolver may be heated by passing it through a heating jacket envelthe mother liquor and which is to be utilized in increasing its capacity for dissolving the potash salts of a new batch of the calcined alunite admitted into the dissolver is further increased by the heat imparted to it by the direct entry of the new batch of hot roasted alunite into the dissolver; so that by reason of the rise of temperature thus pro-- vided, the liquor in the dissolver is in condition to bring into solutionthe potash salts of the new batch. 1

It will be apparent, therefore, that the fundamental or characteristic mode of operation of the process consists in utilizing the heat of the roasted alunite to bring the liquor in the dissolver to so high a temperature that it will have the maximum dissolving capacity for potash salts, and to recover the major portion of the potash salts thus dissolved by cooling the solution thereby decreasing its capacity for maintaining the potash salts in solution, and again restoring the liquor to a capacity for taking up in solution the potash salts of a new charge or batch of roasted alunite by once more ralsing its tem-' peratura, utilizing for that purpose the heat of the calcining mass. 1

It is further to be noted that the hot solution of potash salts, on its way through the cooling tower undergoes considerable evaporation and this evaporation likewise contributes toward the depositing out of the potash salts from the mother liquor. In the cooling tower, the solution is preferably sprayed downwardly through an upwardly risin current of atmospheric air, which may be ad i nitted at ordinary atmospheric temperatures and which, moving in a current crating effect referred to.

It will be understood that after the potash salts have been lixiviated out of the roasted alunite, the residue, that is to say, the alumina, is removed in any suitable manner from the dissolver and is washed to recover any of the potash salt solution contained in it, and that these washings may be conveniently returned to the dissolver, serving to replenish the water lost in the stated evaporation.

In the accompanying drawing is indicated, diagrammatically, a general arrangement of apparatus suitable for'the practice of the invention.

Referring to the drawing, A indicates an elevator for raising the raw or'unca'lcined alunite into the feeding bin B, from which it is discharged into the preheater C of the end is indicated at E. From the muflie fur nace', the fumes pass at a into an. acid condenser F. G represents the dissolyer and b the feeding device for removing the alumina therefrom. All of these parts are fully described and illustrated in my application Ser. No. 7 66,269 hereinbefore referred to.

From the dissolver Gr an overflow 0 conveys the hot solution of potash salts into the receiving tank H .from which it is pumped by the pump d into the filter I. From the filter the "hot solution passes through the tank J from which it is sprayed down through the cooling tower K against an upwardly rising current of atmospheric air. The slush from the cooling tower is rein the drawing, to the dissolver after first passing through the jacket of the dischargc portion E of the muffle" furnace, and, as.

hereinbefore explained, is heated thereby before again entering the dissolver. The alunite, hot from the heat of calcining is dropped into the aqueous solvent in the dissolver, and adds heat directly thereto.

The alumina from the dissolver is re-. moved, after lirdviation into -a receiving tank'R and is pumped therefrom by a pump 6 into a filter and washers. The first washings from thi filter are returned to the dissolver and thefinal washings to a sewer, as indicated. The solids, i. 6., the washed alumina) pass from the filter S into a feedhopper 7, thence to a drier T and finally to a receiving U.

., In connection with the fcregoing and eventually to a storing tion, of apparatus appropriate to the practice of the-invention, it willbe understood that I do not limit myself toany specific form or modification thereof.

' Theavailability of the/invention for suc-. cessful commercial practice is based largely upon the circumstance that the solubility of the potash salt (potassium sulfate) in water at 100 'C. is more than twice as great as its solubility in Water at 20 0., so that the recovery of the potash is dependent upon this difference in solubility assisted by the evaporation effected in the cooling tower.

' A dissolver of the Hendrix type may be used for the purposes of that element of theconstruction and in starting the operation the dissolver contains water. During the subsequent stages of theoperation it is filled, as hereinbefore indicated, with the mother liquo-r returned from the cooling tower and .mufile furnace D whose jacketed discharge which is, in fact, a solution of potassium sulfate. To this solution which represents a saturated solution at ordinary tempera tures, small amounts of wash water from other stages ,of the process are added in the dissolver as has been described. In my op-v eration hereinbefore referred to, I prefer to construct the dissolver with an inclined bot-- 1 tom and with a revolving screw which serves to remove the alumina and discharges into'the receiving tank. Sufiicient water is added to the alumina in the receiving tank to make it fluid so that it can be pumped into the filter, which may be a filter of the Sweetland type. 60% of the weight of water 'is ordinarily sufiicient for the purpose.v In the filter, the alumina is washed until practically free from potash salts, whereupon the first filtrate and the washingscontaini potassium sulfate are returned to the issolver, as described, along with the mother liquor which has come from the centrifugal mass. The final washings of the filter containing aninsignificant amount of salts are run to waste inthe sewer or otherwise.

What I claim is:

1. The process of producing potassium sulfate and alumina from alunite, which comprises introducing hot, calcined alunite into an aqueous solvent, thereby raising the 7 temperature of the solvent and increasing its capacity to dissolve potassiumssulfate, re-

moving'the hot solution of potassium sulfate from theundissolved alumina, cooling the said hot solution, and recovering the potassium sulfate which separates out when the solution is cooled; substantially-as described. 2. The process of producing potassium sulfate and. alumina from alunite, which comprises passing the calcined alunite, while still hot "fromthe heat of calcining, into an salts thereby, filtering the solution, conduct-' ing' thefilterecl solution through a cooling aqueous solvent, lixiviating out the potash tower, thereby precipitating potash salts In testimony whereof I aflix my signature,

therefrom, removing the mother liquor from in presence of two Witnesses.

the separated salts and returning the fil- HOWARD F. CHAPPELL. tered condensed mother liquor to the dis- Witnesses: 5 solver to lixiviate a further portion of cal- M. A. BILL,

cined alunite; substantially as described. M. L. BOWEN. 

